Dome-shaped electric furnace roof construction



Juile 10, 1969 WHANSEN ET AL 3,448,703

DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Filed Dec. 26. 1967 SheetINVENTORS. AEWA/'T/I 1144 44 55 W/LLMMC 720201? v lrram/vzf m 1 R Z W 60 r. 2 mm m6 6 M June 10, 1969 K. w. HANSEN ETAl 3,448,703

DOME-SHAPED ELECTRIC FURNACE ROOF CONSTRUCTION Filed Dec. 26. 1967.Sheet of 2 INVENTORS'. mam 5mm #mvsew BYW/LL/AM c 74mm? MZIAflMATTOAIVEY United States Patent 3,448,703 DOME-SHAPED ELECTRIC FURNACEROOF CONSTRUCTION Kenneth W. Hansen, Bethel Park, and William C. Taylor,Pittsburgh, Pa., assiguors to Dresser Industries, Inc., Dallas, Tex., acorporation of Delaware Continuation-impart of application Ser. No.533,725, Mar. 4, 1966. This application Dec. 26, 1967, Ser. No. 701,514

Int. Cl. F23m 5/02; H051) 7/18; F23d 1/00 U.S. Cl. 110-99 7 ClaimsABSTRACT OF THE DISCLOSURE A dish-shaped dome type furnace roofcomprising basic refractory shape arranged in concentric rings, aportion of which comprise metal encased shapes covered by a contourcontrol structure and the remainder of which comprise shapes mortaredtogether.

Related case This case is a continuation-in-part of our application Ser.No. 533,725, filed Mar. 4, 1966, having the same title, now abandoned.That application has been abandoned favor of this application.

Background A good treatise on the subject of electric furnaces, theconstruction of roofs therefor, and the like, is Electric FurnaceSteelmaking, Volume 1, Design, Operation, and Practice, published byInterscience Publishers, a division of John Wiley & Sons, Inc., in 1962.It is a product of the Physical Chemistry of Stcelmaking Committee ofThe American Institute of Mining, Metallurgical, and PetroleumEngineers. The reader is directed thereto for a discussion of knownprior art and, in particular, the section entitled Roof Construction,beginning on page 163. As this work points out, silica brick and, to alesser extent, certain types of firebrick and high alumina brick havebeen the conventional refractories for the roofs of electric steelmakingfurnaces. However, with increasingly severe and extended furnacecampaigns becoming conventional, such brick are proving of insuflicientrefractoriness. Basic brick would seem to provide the logicalsubstitute, but usage thereof has been considered replete withdifficulties. First, the very appreciable increase in density as onemoves from silica (about 120 p.c.f.) or one of the more dense highalumina brick (for example, about 160 p.c.f.) to basic (180+ p.c.f.)brick so increases the total weight of a given roof that much existingroof lifting and moving equipment is insufficient. However, in now orrefurbished shops (or, of course, in those with large enough movingequipment) this is overcome and, thus, it is an object of this inventionto provide a basic refractory roof construction of the type used forelectric furnaces and the like.

In United States Patent No. 2,814,476, there is illustrated one priorpublished suggestion of a possible construction for a basic electric arcfurnace roof in which all of the brick between electrode mounts and whatare termed abutment brick are suspended from a rather complicatedarrangement of interconnected steel work to form a flat roof.

Others have also suggested a suspended flat-type roof construction forthe electric arc furnace but, as far as we know, none has ever beeninstalled and operated successfully. In any even, one problem with suchflat roof construction is that when a furnace is tilted (and tilting toan angle of 40 is not out of the ordinary) this puts 3,448,703- PatentedJune 10, 1969 can cause a short circuit of the furnace. This can be, inI large part, mitigated by avoiding use of carbon steel anywhere withinperhaps six feet of the center of the roof. Nonmagnetic stainless steelcan be a useful device.

Brief description of the invention The present invention providescooperating hold-down contour structure for a novel arrangement of basicrefractory brick in a downwardly opening dome-shaped roof configuration.The arrangement overcomes the various prior art difiiculties outlinedabove. Briefly, a roof according to this invention is comprised of aplurality of abutting rings of basic brick contained Within a circularroof band in a downwardly opening domed configuration. A portion of thebrick in the roof which are arranged in the rings between the band, butstopping short of the electrode ports, are metal cased brick; forexample, of the type disclosed and claimed in United States Patent No.3,180,744, the preferred embodiment described in column 5, beginningline 58. By a portion, I mean at least two rings of brick adjacent theband are metal encased. It is preferable if a majority of the brick inthe roof are metal encased. The metal casing is preferably of thegeneral type shown in United States Patent No. 2,736,187. The remainderof the brick in the roof can be of the same type but they are not metalcased. They are laid up with refractory mortar. A preferred mortar iscomprised approximately of about 40% ball mill fine dead burnedmagnesite, about 50% pigment grade iron oxide, and about 10% of sodiumsilicate. Other refractory mortars comprising finely ground refractoryaggregates such as calcined fire clay, calcined bauxite or chrome ore ormagnesite and a suitable binder such as clay and sodiumsilicate may beused. Suitable binders for refractory mortars are described inCementitious Bonding in Ceramic Fabrication, chapter 18, CeramicFabrication Processes, edited by W. D. Kinary (1958). The mortar isapplied as a bed joint between adjacent rings, and as a dipped jointbetween brick in a common ring. The remainder of the center area aboutthe electrode portion is rammed in place. We prefer a high aluminacomposition called Korundal Plastic, a high alumina ramming mix.

The metal cased brick are provided with means to allow expansion, as isdiscussed in more detail below. In addition, there is provided contouredhold-down structure arranged to prevent upward movement of the roof whenit is heated. The roof is in compression when heated.

Detailed description A better understanding of the invention and otherfeatures and advantages thereof will become readily apparent from astudy of the following detailed description, with reference to theappended drawings. In these drawings:

FIG. 1 is a sectional side elevation of the roof of FIG. 2, taken alongthe line AA;

FIG. 2 is a top view of a roof construction according to this invention;

FIG. 3 is an isometric view of one of the metal encased brick used infabrication of the roof of FIGS. 1 and 2; and,

FIG. 4 is a schematic diagram of an alternative holddown structuredesign.

Before describing the drawings in detail, it should be understood theyshow but one manner of practicing this invention and thus are intendedas exemplary only and not limiting since the true measure of the spiritand scope 3 of this invention is as defined in the hereafter appendedclaims.

In FIGS. 1 and 2 there is shown a plurality of rings, numbered 1 through19, arranged circumferentially within the circular roof band 20. Rings 1through 11, all of the full rings, are fabricated of metal encased brickof the type shown in FIG. 3. The remaining partial rings, 12 through 19,are of uncased brick. Sequential rings 12 through 19 are joined byapproximately A of mortar. Each of the electrode ports 22, 23, and 24are fabricated of a plurality of refractory arch brick; for example, ofthe type disclosed and claimed in United States Patent No. 3,210,206.These brick are also laid up with a & mortar join-t. Contoured hold-downmembers 25 extend across equidistant chords of the circle formed by theband 20 to hold down substantially all rings of the metal encased brickin those areas where distortion is most likely to occur. In FIG. 2, wehave shown but three of these members. An even more satisfactoryarrangement is shown in FIG. 4, which illustrates an intersectingarrangement of contour members 25A generally in the form of a sixpointedstar. The ends of the reinforcing members 25 or 25A are suitably affixedat their respective ends to the retaining band 20. They can bespring-loaded to allow for some upward movement of the roof; forexample, a spring of sufficient strength as to allow only about /2 risein the roof. Alternatively, the contour member can be spaced about 1 or/2 above the cold roof, thus allowing for a /2 rise when the roof isheated. The center area 35 is of a rammed refractory monolith.

When the furnace is placed in service, adjacent metal cases in the metalencased brick rings oxidize and react with each other and adjacent brickforming a monolithic structure over the hot face. In the more centraluncased rings the mortar likewise reacts with adjacent brick, wherebyall of the brick in the roof are joined in a monolithic structure overthe hot face. When an iron oxide containing mortar is used in the innerrings, joints of similar (predominantly magnesio-ferrite) chemicalcomposition are formed over the entire roof between brick without thedanger of inducing an electrical current through metal cases.

There is provision for both circumferential and radial expansion. As canbe seen by reference to FIG. 3, each of the brick has an expansion crimp50 formed on the flat side adjacent its hot face and an additional crimp51 formed on one edge adjacent the hot face. A single crimp 52 is formedadjacent the cold face of one fiat side of each brick. It is preferablethat the crimps 50 and 52 be on the same flat face to simplifybricklaying. This arrangement provides for both radial andcircumferential expansion over the hot face and circumferentialexpansion over the cold face of each ring.

Also note that the three partial segments of ring 19 abut substantiallycentrally about the vertical axis of the roof. This arrangement providesincreased strength until the roof is burned in and the rammed materialacquires a ceramic bond therethrough.

The shapes of the respective brick of each ring are dictated byconventional practice as, for example, shown in page 507 of the bookModern Refractory Practice, 4th

edition, published by the Harbison-Walker Refractories Company in 1951.

Having thus described the invention in detail and with sufficientparticularity as to enable those skilled in the art to practice it, whatis desired to have protected by Letters Patent is set forth in thefollowing claims:

We claim:

1. In an electric furnace or the like having a downwardly openingdish-shaped dome-type roof, said roof being fabricated of a plurality ofbasic refractory shapes contained in adjacent rings within a band, saidshapes arranged in a series of concentric rings, a portion of the Ibrick forming adjacent rings and extending from said hand towards thecenter of said roof being metal encased basic refractory brick, theremainder of the brick forming the remainder of the rings being uncasedbasic refractory brick joined by a refractory mortar, said metal encasedbrick having means arranged to allow for expansion upon heatup of saidroof, there being contour controlling hold-down structure oversubstantially all of said metal encased rings.

' 2. In an electric furnaceor the like having a downwardly openingdish-shaped dome-type roof, said roof being fabricated of a plurality ofbasic refractory shapes contained in adjacent rings within a band, saidshapes arranged in a series of concentric rings, a major portion of thebrick forming adjacent rings and extending from said band towards thecenter of said roof being metal encased basic refractory brick, theremainder of the brick forming the remainder of the rings being uncasedbasic refractory brick joined by a mortar characterized by a substantialproportion of iron oxide, there being sufficient iron oxide to reactwith adjacent basic brick to form a monolithic hot face, said metalencased brick having means arranged to allow for expansion upon heatupof said roof, there being contour controlling hold-down structure oversubstantialy all of said metal encased rings.

3. The roof of claim 1 in which said cased brick include means adjacentthe cold face thereof allowing for circumferential expansion, and meansadjacent the hot face thereof allowing for both radial andcircumferential expansion. 4. The roof of claim 2 in which the meanswhich allows for expansion at both the hot face and the cold face iscomprised of expansion crimps formed from the metal of which the metalcases are made.

5. The roof of claim 1 in which the hold-down structure is comprised ofa plurality of arched members extending across substantially equidistantchords of the band.

6. The roof of claim 5 in which the arched members are arranged to allowon the order of about A." rise in the roof upon heat-up.

7. The roof of claim 5 in which there are three of said arched members.

References Cited UNITED STATES PATENTS 2,304,170 12/ 1942 Heuer.3,139,048 6/1964 Hall. 3,367,292 2/1968 Woodruif et al. -99

FREDERICK KETTERER, Primary Examiner.

